Single, isolate (solitary) rods and cones will be obtained by enzymatic dissociation of the tiger salamander retina and kept in vitro for several days during which time the effects of cyclic GMP and calcium on the generator (dark) current will be studied. The effects of agents that affects the intracellular concentrations of both compounds will also be studied. Experiments will be done under voltage clamp conditions and drugs delivered to the cells through the second barrel of a double-barrel micropipette. The role of cyclic GMP or calcium as the internal messenger will then be assessed. For solitary cones, the electrical properties of spectrally-identified cells will be studied. Cultures of mature retinal neurons will be prepared and identified cells used to investigate aspects of cell-cell interaction and synapse formation. Cell identification will be made using morphological, pharmacological, histochemical and immunological methods. Electrical properties, using standard electrophysiological procedures, will be established before and after identifid cells contact one another. Tests for synaptic connections will be made using intracellular techniques and the identity of chemical transmitters established using, primarily, pharmacological tools. These studies might provide information on the possible underlying mechanisms involved in the funcional organizatin of the intact, vertebrate retina.